Electropneumatic sound reproducer



Feb. 3, 1948. w. c. EAVES ELECTROPNEUMATIC SOUND REPRO DUCER Filed July 25, 1942 2 Sheets-Sheet 1 INVENTOR W 4 W FIC3.4.

C01 TTORNEY Feb. 3, 1948. w. c. EAVES 2,435,534

ELECTROPNEUMATIC SOUND REPRODUCER Filed July 2 5, 1942 2 Sheets-Sheet 2 lglfe 664W ATTORNEY Patented Feb. 3, 1948 "ELECTROPNFUMATIC SOUND REPRODUCER William C. Eaves, Elyria, Ohio, assignor to Eaves s-Sound Projectors,-.Inc., New York, N. Y., acorxporation of "Delaware Application July '25, 1942, Serial No. 452,269

- 9 Claims.

This invention relates'to soundproducing apparatus and more particularly to apparatus of the type wherein a fluid stream is'modulatedto generate sound waves.

One of the objects of the present invention'is to provide novel imeans vformodulating a stream or current of expansible fluid so as to impart sound producingcharacteristics thereto.

Another object is'to provide a novel modulating valve 'for a sound head of the air .flowtype and a novel voice coil arrangement for actuating said valve.

AJfurther object is toprovide anovel means for mounting and controlling the operation of the movable grid'of the modulating valve of an air head.

Still another object is to provide the above means with novel apparatus for counter-balancing the effect on the movable grid of thepressure of the fluid stream.

A still further object is to-provide a novel grid valve for a sound head of "the air flow type, said valve being so constructed that angular oscillation of the movable grid thereof about an axis parallel to and centrally disposed relative to'the air stream is adapted to produce the desired modulation of said stream.

Still another object .is to provide novel means for mounting the above valve to facilitate the adjustment and assembly'thereof.

A still further object is to provide a novel sound producing apparatus of the air flow type adapted to reproduce and amplify speech and music to render the latter audible .for ,a great distance without any appreciable diminution of the fidelity of reproduction.

The above and further objects and novel features of the invention will more .fully appear from the following detailed description when the same is read in connectionwith the accompanying drawings. It is to be expressly understood, however, 'that'the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

In the drawingawherein like reference characters refer to like parts throughout the several views,

Fig. 1 is a sectional view taken in a vertical plane through the axis of one type of sound'head embodying the" present invention;

Fig. 2 is a top plan view'ofthe modulating valve and Voice coil assembly of the soundlhead of Fig. 1;

Fig. 3 is a sectional view taken substantially along line 33 of Fig. 1';

Fig. 4is a sectional view, with parts broken away, taken in a vertical plane along the axis of a sound head embodying another form of the present invention; and I Figs. 5 and 6 are sectional views similar to Fig. 1 of sound heads embodying modified forms of the invention.

Referring to Fig. 1, .the'novel sound ihead'illustrated therein comprises" a cup-shaped casing'zil provided with a flanged upper end to whichis secured a cover plate 2|, the latter having mounted thereon a suitable sound propagating device, suclras an eXponental horn 22, and-being provided with'a'central recess 23 which connects said horn with the casing interior. Rigidly mounted in a vertical plane insaid casing is a permanent magnet 24 which hasipoles 24a thereof adjoining plate 2|, said poles preferably terminating on opposite'sides'of recess 23 with the ends thereof curved and in approximate alignment with saidrecess. A hollow, cyindrical member'25 of suitable magneticmaterial, having an enlarged externally threaded base'portion 25a, 'is centrally mounted in casing 20, preferably by having said base portion threaded into a recess '26 provided in thebase-of magnet '24. The upper end-of .member '25 is located between the ends of poles 24a, being concentric therewith and spaced only a short-distancetherefrom to provide a path of decreased reluctance for the flow of magnetic flux between said poles. An externally threaded lock nut 261) may be threaded into recess 26 to engage the lower face of member 25 in order to fix the latter against inadvertent angular displacement.

The interior of member 25 serves as a fluid chamber and air under pressure is admitted therein through a suitable inlet conduit 2'! which "is preferably flexible and which, in the form illustrated, connects at one end with said member and at the other end with a source of compressed air (not shown). The lattermay be a pump disposed some distance from the sound head, in which event it will be desirable to provide a'valve (not shown) in conduit '21 adjacent casing 26, said valve being adapted to close said conduit to maintaina line .pressure above atmospheric therein when the sound head actuating means is inoperative.

To produce sound waves in horn22, the airflow .into said horn from member 25 is modulated by a novel grid valve'arrangement disposed at the upper end of said member in the path of the air stream as the latter enters the horn. In the form illustrated, said valve means comprise a circular, stationary grid 28, secured to the upper end of member 25, for example, by screws 2%, and provided with a plurality of radial slots 28a spaced equally around the center of said grid (Fig. 3). Mounted for oscillation relative to said grid in a manner more fully described hereafter is an inverted cup-shaped grid member 29, 3!; comprising a disc 29 parallel to said grid and spaced a slight distance therefrom and a cylindrical wall 35 depending from said disc to surround the upper end of member 25 in the air gap between said member and the endsof magnet poles 24a. For facilitating the winding of a voice coil on member 29, 30 in a manner more fully described hereinafter, wall 32 preferably has the lower end thereof projecting beyond the lower edges of poles 24a, said projecting portion being flared outwardly to provide a widened base edge 30a which has a groove 391) formed therein. Disc 29 constitutes the rotary grid of the modulating valve, being provided with a plurality of radial slots 290. (Fig. 2) adapted for cooperation with slots 28a for the purpose of controlling the total port area available for air flow out of member 25. Variations in this port area effected by movement of grid 29 relative to grid 2?; modulate the air stream so that by suitably controlling the oscillation of grid 29 a desired wave fre quency within the audible range may be imparted to said stream.

In order to reinforce disc or grid 29, which is relatively thin, and prevent buckling at the center thereof, it is preferable to provide a plurality of radial ribs 2% in the upper face of said grid at predetermined points between slots 29a, four such ribs being shown in the illustrated embodiment (Figs. 1 and 2). As shown, said ribs decrease in height as the same approach the center of said grid and are preferably connected at the outer ends thereof to an annular ridge or flange 290 formed in the upper face of said grid between the periphery thereof and the outer ends of slots 29a.

In order to mount grid member 29, 31) for oscillatory movement relative to grid 28, a stub shaft 3| is secured at the upper end thereof to the center of grid 29, forexample, by a press fit or by being soldered thereto. Shaft 3| projects downwardly through a recess 32 in the center of grid 28, and the walls of said recess are adapted to serve as a journal therefor. Rigidly secured to the lower end of shaft 3| is a torsion rod 33 which projects downwardly through the center of member 25 and is fixed at its lower end to the central portion of a diaphragm 34 by suitable means, such as a tapered and threaded split chuck 31 mounted on said diaphragm and a tapered nut 38 threaded on said chuck. To dampen and substantially eliminate resonant vibrations in torsion rod 33 in a direction perpendicular to the length thereof, it is preferable to surround said rod with a suitable sheath 33a of non-resonant material, such as a strip of radio wire spaghetti which extends from chuck Bl to the lower end of shaft 3i. Diaphragm 34 is held in fluid-tight engagement with a shoulder 39 formed in base portion 25a of member 25 by an annular member 35, which engages the edges of said diaphragm and is in turn secured to shoulder 39 by screws 36, thereby sealing the lower end of said member. The effective area of diaphragm 34 is slightly greater than the area of grid 29 so that said diaphragm 4 acts through rod 33 to counter-balance the force applied by the fluid in chamber 25 on grid 29 and tends to urge the latter grid into contact with grid 23.

To overcome in part the pressure exerted by diaphragm 34 on grid 29 and permit the latter to assume an operative position wherein it is spaced a short distance from the upper face of grid 23 and also to control this axial spatial relation between the grids, novel adjustable control means are provided for exerting an upward pressure on diaphragm 34. As shown said control means comprise a hollow casing or cylinder 49 threaded into a recess 4! in the lower end of casingze, the latter being provided with an inwardly projecting cup-shaped portion 28a at the upper end of which said recess is formed.

As a result, cylinder 42 has the lower end thereof above the bottom surface of housing 2%. Cylinder 50 extends vertically upward through recess ll in the direction of diaphragm 34 and a piston 22 is slidably mounted in said cylinder, said piston having a rod 43 fixed to or formed with the up er face thereof and extending through a recess in the upper end of said cylinder. The tip 43a of said rod, which is adapted to engage the lower end of nut 38, is preferably formed of a non-resonant material, such as hard rubber. Engaging piston 62 to apply an upward yielding force thereto is a spring 44 disposed between said piston and a plug or screw 25 threaded into the lower end of cylinder 42. The pressure applied by said spring against diaphragm 3 may be controlled by axial adjustment of plug 45 relative to said cylinder or by axial adjustment of said cylinder relative to housing 29. To prevent inadvertent movement of the cylinder, a lock nut 49a is preferably screwed on the threaded shank of said cylinder to engage the face of the upper end of indented portion 2011.

In order to actuate movable grid 29 for pivotal vibratory movement about the axis of torsion rod 33 in accordance with electric current undulations produced in a conductor by a source of sound, a voice coil to, which constitutes the conductor, is wound in a novel manner on grid member 29, 3Q. In the form shown, coil 26 comprises horizontal portions 45a and 4627 (Figs. 2 and 3) which extend across the upper and lower ends, respectively, of said grid member, and portions Mic which connect said horizontal portions and extend vertically along the sides of wall 36 in the air gap between poles 24a and the periphery of said wall. Upper portions a of the windings are preferably directed across the face of grid 29 in arcuate paths between the outer edge of said grid and annular ridge 29c, thereby avoiding slots 29a. For purposes of clarity, the windings are somewhat diagrammatically shown in Figs. 2 and 3, it being understood that actually vertical portions 350 of successive windings are in contact with each other, providing a greater number of windings than is illustrated. Lower horizontal portions 461) of the windings (Fig. 3) are disposed in groove 38b in the divergent lower edge 32a of wall 28. It is preferable to secure portions 46a and 46b in operative position relative to each other and to member 23 and 38, for example, by

embedding said portions in a suitable insulating I compound having adhesive properties, said compound being solid at the temperatures to which the voice coil windings are raised during operation of the sound head and being applied to said windings after the latter are operatively positioned on said member.

To modulate the air stream flowing through grid valve 28, 29 in accordance with the cur-rent undulations in coil 56 so as to reproduce with true fidelity the sound waves which initiated said undulations, slots or ports 28c and 29a are so designed that the degree of opening thereof Will be directly proportional to the angular displacement of grid 29 relative to grid 28. One arrangement for achieving this result is shown in Figs. 2 and 3 wherein the slots in each of the grids are similar in shape and disposedin a like relation to the grid area, the side walls of each slot being radial and the end walls concentric with respect to the axis of rotation of grid 29. To obtain a maximum degree of fidelity in sound reproduction, it is desirable to restrict the throatof horn 22 to a cross-sectional area equal to the total port area of grid valve 28, Hand to have this horn portion of'minimum area located close tosaid valve.

In operation, air at a pressure exceeding atmospheric is admitted into chamber 25 through conduit 2i and flows in a stream from said chamber through grid valve 23, 2S into'horn 22. The unmodulated electrical current in coil 46, when the latter is energized, provides a magnetic torque which, together with rod 33 and'the air stream, act to establish a neutral position for grid 29 relative to grid 28, said grids being assembled so that in this equilibrium or neutral operative position, ports 213a and 2% are approximately half open. Current modulations in voice coil 46 cause grid 29 to rotate relative to grid 28, thereby modulating the air stream and generating sound waves therein in accordance with the current modulations. It is to be noted that assembly and ad justment of the sound head are greatly facilitated in the above-described structure since grid memher 2%, 36, grid 28, and diaphragm 34 can be operatively mounted on member 25 and adjusted relative to each other before the latter member is threaded into operative position in magnet 24. ihe novel construction of the sound head permits independent radial and axial adjustments of grid 29 relative to grid 28 and permits angular adjustment of member 25 relative to magnet poles 24a. Cylinder and piston mechanism at, 41-; provides a ready and simple means for controlling the axial adjustment of grid 29 relative to grid 28 after the unit has been assembled.

It is tobe understood that the movable grid may be mounted on the high pressure side of the valve, for example, as shown in Fig. 4, wherein a stationary grid is secured between horn 22 and cover plate 2! and a movable cup-shaped grid member 5t, 52, comprising grid 5! and cylindrical wall '52, is mounted between the upper, open end of member 25 and grid 5B. Member 5!. 52 is'like member 29, 30 of the above-described embodiment except that ribs 5!?) thereof are preferably located on the highpressure side of movable grid iii, It is to be understood that in this and the following views the voice coil'is wound on the movable grid member as described in de tail above and illustrated in Figs. 2 and 3.

Means for mounting grid member 5|, 52, for angular oscillation are provided and, in the form illustrated, comprise a jewel bearing 53 of the type Well-known in the watchmakers art, said bearing having the journal thereof located centrallyin the lower face of grid 5% and the pivotal portion carried by a member ti l mounted in the center of grid 5| and rigidly secured to the latter,

for exampleby a press fit.

"Fig. 1, being connected to torsion rod 33, which, in turn, is preferably connected to a diaphragm member subject to adjustment by suitable control means, as shown in Fig. 1. In operation, the diaphragmis adjusted to apply a force to torsion rod 33 which is slightly less than the force exerted'by the air pressure on grid 5! and, as a result, the elements ofbearing 53 are kept in operative engagement with each other controlling the axial relationship between the grids.

Another embodiment of the invention provided with a modified mounting for the lower end of the torsion rod is shown in Fig. 5 and comprises a central member 25 having a grid valve and voice coil assembly at the upper end thereof similar in structure to that shown in Fig. 1. Base 25a of said member is threaded into recess 26 of magnet 24 and has a central recess 55 formed therein through which the lower end of torsion rod 33 extends. To mount said rod, a plate 56 is rigidly secured, as by screws '51, to a shoulder efl'formed in magnet 24 beneath recess 26, said plate being held in fluid-tight engagement with said shoulder. To insure fluid tightness, suitable means, such as a gasket (not shown), may be interposed between said shoulder and said plate. Threaded in a recess 59 provided in the center of said plate is a plu Bl! having suitable holding means, such as a split chuck mount 6 I, 62, secured to the lower face thereof for receiving the lower end of rod 33, tapered chuck SI of said mount being preferably formed with said plug. The end of'said rod held by said mount projects beyond the lower end of the latter and can be engaged and adjusted by a suitable toolonce nut 62 is loosened,

Another embodiment of the sound head is shown in Fig. 6 wherein a torsion ribbon 63 is substituted for torsionrod 33 of Fig. 5 and suitable means are mounted in plate 56 to operatively secure the lower end of said ribbon. The latter means comprise a plug 64 threaded into recess 53 and provided with an elongated slot 65 conforming substantially to the cross section of said ribbon whereby the latter, when extending through said recess, is held against angular movement. To secure said ribbon against axial movement, a set screw 86 is preferably threaded into the lower end of plug M for engagement with the face of said ribbon. By loosening said screw, the tension in ribbon 63 as well as the axial position of grid 29 during operation can be adjusted and by rotating plug 64 angular adjustment of said ribbon and, therefore, of grid 29 can be effected.

There is thus provided a sound head having a novel fluid modulating valve so actuated and mounted as to obtain sound reproduction of a greater fidelity and a greater degree of amplification than has heretofore been possible in sound reproducing devices of the air flow type. There is also provided a novel voice coil and grid assembly whereby vibration transmitting linkages between the magnetically actuated armature and the vibratory member of the valve are eliminated, making possible a faithful reproduction of sound over a wide range of audible frequencies. Novel means for mounting a movable valve member for angular, oscillatory movement in a plane perpendicular to the air stream being modulated thereby are provided, as well as novel means for readily controlling the equilibrium position 7 of said member. Furthermore, a novel arrangement of ports in the movable and stationary grids of a fluid modulating valve is provided whereby the total fluid passage area of the valve varies directly with the angular displacement of said movable grid from equilibrium position.

Although several embodiments of the present invention have been illustrated and described, it is to be expressly understood that the same is not limited thereto. For example, it will now be apparent to those skilled in the art that holding means other than the conventional split chuck type means shown might be utilized for securing the ends of th torsion rods. Various other changes may be made in the design and arrangement of parts without departing from the spirit and scope of the invention. For a definition of the limits of the invention, reference is primarily had to the appended claims.

What is claimed is:

1. In a sound head wherein a stream of fluid is modulated to generate sound waves, means comprising a passage for said stream, grid valve means interposed in the path of said stream at the discharge end of said passage, said valve means comprising a movable member carrying a disc-like rotary grid, the latter extending across said fluid stream, means for mounting said movable valve member for pivotal movement about the central axis of said grid, said mounting means comprising a torsion member, means for connecting one end of said torsion member to said grid and means for fixing the other end of said torsion member against angular movement, and electro-magnetic means for actuating said movable valve member to modulate the fluid stream, said electro-magnetic means comprising a voice coil wound on said movable valve member and a permanent magnet having the poles thereof disposed diametrically opposite each other and adjacent said valve member.

2. In a, sound head wherein a stream of expan sible fluid is modulated to generate sound waves, means comprising a passage for said stream, valve means interposed in the path of said stream at one end of said passage, said valve means comprising a stationary grid and a rotary grid member, means for mounting said rotary grid member for movement about an axis parallel to and centrally disposed relative to said stream, said mounting means including a torsion member, means for connecting one end of said torsion member to said rotary grid member and adjustable means for rigidly securing the other end of said torsion member against axial movement, and means for actuating said rotary grid mem ber to modulate the fluid stream, said last-named means comprising a permanent magnet and a voice coil wound on said rotary grid member. 3. In a sound head wherein a stream of fluid is modulated to generate sound waves, means comprising a passage for said stream, grid valve means interposed in the path of said stream at the discharge end of said passage, said valve means comprising a cup-shaped movable member carrying a disc-like grid, means for mounting said movable valve member for pivotal movement about the axis of said grid, said mounting means comprising a torsion ribbon, means for connecting one end of said ribbon to said grid and adjustable means for rigidly securing the other end or said ribbon against movement, and electromagnetic means directly associated With said movable valve member for actuating the latter to modulate the fluid stream.

4. In a sound head wherein a stream of expansible fluid is modulated to generate sound waves, means comprising a passage for said stream, valve means interposed in the path of said stream at the discharge end of said passage, said valve means comprising a stationary grid and a rotary grid disposed exteriorly of said stationary grid and the discharge end of said passage, means for mounting said rotary grid for angular movement about an axis parallel to and centrally located relative to said stream, said mounting means comprising a bearing carried by said rotary grid and projecting through said stationary grid and having the journal thereof formed in said stationary grid and a torsion member adapted to yieldingly oppose angular movement of said rotary grid from a neutral position, and means for actuating said rotary grid for oscillatory movement to modulate said stream.

5. In a sound head of the type wherein a stream of expansible fluid is modulated to generate sound waves, valve means interposed in the path of the stream, said valve means comprising a circular grid member having a grid portion, means for mounting said grid member for rotary movement about the center thereof in a plane perpendicular to the fluid stream, said means comprising a torsion member adapted to yieldingly oppose movement of said grid member from a neutral angular position, pressure responsive means connecting with said fluid stream and with the atmosphere and fixed to said torsion member; said pressure responsive means tending to move said grid member in a direction opposite to the direction in which the pressure of the fluid, stream on the grid portion of said member tends tomove it, and means comprising a voice coil carried by said grid member for oscillating the latter to modulate the fluid stream.

6. In a sound head of the type wherein a stream of expansible fluid is modulated, modulating means comprising a rotary grid member having a grid portion, a torsion rod secured to said grid member to oppose movement thereof from a neutral angular position, pressure responsive means connecting with said fluid stream and with the atmosphere and secured to said torsion rod, said pressure responsive means tending to move said grid member axially in a direction opposite to the direction in which the pressure of the fluid stream on the grid portion of said member tends to move it, and electro-magnetic means comprising a voice coil carried by said grid member for oscillating the latter to modulate the fluid stream.

7. In a sound head of the type wherein a stream of expansible fluid is modulated, modulating means comprising a rotary grid member, a torsion means connected to said grid member to oppose movement thereof from a neutral position, electro-magnetic means comprising a voice coil mounted on said grid member, said last-named means being adapted to oscillate said grid member to modulate the fluid stream, and means for adjustably mounting said torsion means to provide a control for the neutral position of said grid member.

8. In a sound head of the type wherein a stream of expansible fluid is modulated, modulating means comprising a rotary grid, a torsion rod secured to said grid to bias the latter to a neutral position, pressure responsive means connecting with said fluid stream and with the atmosphere and secured to said torsion rod, said pressure responsive means tending to move said grid in a direction opposite to the direction in which the pressure of the fluid stream on the grid tends to move it, and electro-magnetic means for oscillating the grid to modulate the fluid stream.

9. In a sound head, a grid valve for modulating a fluid stream to impart sound producin characteristics thereto comprising a stationary disc-like grid and a grid mounted for oscillatory movement about its center in a plane parallel to said stationary grid, said grids each having tapered slots radially disposed relative to the center of oscillation of the movable grid, said slots all being of the same taper so that the total port area. of said valve for fluid passage will 15 7 10 Number vary directly with the angular displacement of said movable grid.

WILLIAM C. EAVES.

REFERENCES CITED UNITED STATES PATENTS Name Date 1,766,612 De Forest June 24,1930 1,940,797 Halvorsen Dec. 26, 1933 2,003,880 Eaves et a1. June 4, 1935 2,141,208 Eaves Dec. 27, 1938 Chandler July 7, 1942 

